AC Dimmer

We all know what an AC dimmer is; for those who don’t, it’s a kind of a circuit which can control the amount of AC voltage to be given to any device. You can see them in a fan regulator or a light dimmer switch.

But have you ever wondered of applying the same concept of regulators/dimmers using a microcontroller? If you haven’t, don’t worry, this project deals with the same stuff.

Prototype of AVR ATMega16 based AC Dimmer

FIg. 1: Prototype of AVR ATMega16 based AC Dimmer

First of all we need to understand the importance of a triac in such circuits. A triac is a 3 terminal device which can control the amount of AC current passing through it. This can be achieved by applying variable AC potential at its Gate pin. Here I’m using BT 136 IC and its pin 3 is the gate pin. For further details please refer to its datasheet.

In our normal regulator switches, this task is achieved by using a potentiometer. But when it comes to digitally handling this situation, potentiometer isn’t a good choice.

Here come these opto-couplers and opto-isolators in action. They become a sort of a bridge between AC and Digital portions. One more important term that I should have introduced earlier is Zero Crossing Detection. This is also very important while digitally controlling the dimmer circuit.

A Zero Crossing is shown in the image below:

Diagram showing zero crossing on typical sine wave AC Waveform

Fig. 2: Diagram showing zero crossing on typical sine wave AC Waveform

It is important to make the microcontroller know about this crossing because this helps in maintaining the dimming status of the device.

Diagram showing clipping of AC waveform with respect to zero crossing

Fig. 3: Diagram showing clipping of AC waveform with respect to zero crossing

This picture above shows us how to accomplish various dimming stages. On attaining the zero cross position the amount of delay given to start up the opto-isolator, determines the average voltage given as an output.

So this is what an opto-isolator is doing, it is firing the triac which indirectly helps in switching on the device. This can be compared to PWM situations in digital electronics.

Now talking about the opto-coupler part, it is helping the microcontroller to detect the zero crossing point. On detecting this, it starts performing the dimming action i.e dealing with the opto-isolator.

A diode is connected to the opto-coupler input so that the LED inside it isn’t reversed biased.

In my coding part I’m using the ADC values to serve as the parameter for the delay().

This concept has a lot of applications in Home Automation wherein you need to control the fan’s speed or light’s brightness.

So to sum up the concept behind the AC dimmer using a microcontroller I would recommend going through the picture below:

Block Diagram of AVR ATMega16 based AC Dimmer

Fig. 4: Block Diagram of AVR ATMega16 based AC Dimmer

REQUIREMENTS:

• ATMega 16 IC

• Optocoupler 4N35

• Opto-isolator M0C3041

• Triac BT136

• 1N4007 diode

• Potentiometer (optional, for ADC input, 50K)

• Resistor values: 330E, 10K, 4.7K

• 220V AC source

• AC device (incandescent bulb)

CIRCUIT DIAGRAM:

Check the Circuit Diagram Tab for complete AC Dimmer Circuit

Project Source Code

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#include<avr/io.h>
#include<util/delay.h>
#include<adc_lib.h> //for ADC purpose
 
void main()
{
 ADCinit(); //initializing ADC 
 int j=0,i=0;
 DDRC=1;
 PORTC=0;
 while(1)
 {
if(!(PINC&(1<<7)) && j==0) //if upper half of the sine wave detected 
{
PORTC&=~(1<<0);
_delay_ms(i);
PORTC|=(1<<0);
j=1;
}
if((PINC&(1<<7)) && j==1)  //if lower half of the sine wave detected
{
PORTC&=~(1<<0);
_delay_ms(i);
PORTC|=(1<<0);
j=0;
}
i=(read_adc(0)/105); //i=[0 to 9]
 }
 } 
 
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